Messages in this thread | | | Date | Tue, 19 Feb 2002 18:11:26 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [RFC] Page table sharing |
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On Tue, 19 Feb 2002, Linus Torvalds wrote: > On Tue, 19 Feb 2002, Daniel Phillips wrote: > > > > > > At that point you might as well make the TLB shootdown global (ie you keep > > > track of a mask of CPU's whose TLB's you want to kill, and any pmd that > > > has count > 1 just makes that mask be "all CPU's"). > > > > How do we know when to do the global tlb flush? > > See above. > > Basically, the algorithm is: > > invalidate_cpu_mask = 0; > > .. for each page swapped out .. > > pte = ptep_get_and_clear(ptep); > save_pte_and_mm(pte_page(pte)); > mask = mm->cpu_vm_mask; > if (page_count(pmd_page) > 1) > mask = ~0UL; > invalidate_cpu_mask |= mask; > > and then at the end you just do > > flush_tlb_cpus(invalidate_cpu_mask); > for_each_page_saved() { > free_page(page); > } > > (yeah, yeah, add cache coherency etc).
It's a little worse than this, I think. Propagating pte_dirty(pte) to set_page_dirty(page) cannot be done until after the flush_tlb_cpus, if the ptes are writable: and copy_page_range is not setting "cow", so not write protecting, when it's a shared writable mapping. Easy answer is to scrap "cow" there and always do the write protection; but I doubt that's the correct answer. swap_out could keep an array of pointers to ptes, to propagate dirty after flushing TLB and before freeing pages, but that's not very pretty.
Hugh
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